Screening effect for excitonic spectrum of Coulomb coupling between two Dirac particles

The properties of screening effect for energy spectrum of excitons in monolayer transition metal dichalcogenides are investigated using a multiband model. The excitonic hamiltonian in the product base of the Dirac single-particle is used. The corresponding energy eigenvalue system of the first order ODE (radial equations) was solved using the finite difference method. This enables to determine the energy eigenvalues of the discrete excitonic spectrum and the wave functions. We compare the results for the energy spectrum and the corresponding eigen-functions forms for WS 2 and WSe 2 computed for two different potentials: pure Coulomb and screened Coulomb (Keldysh potential). It is demonstrated that excitonic energy levels for unscreened potential lie dipper, and the corresponding eigen-functions’ forms differ from those obtained for screened one.

Revisiting neutron yield in table-top nuclear fusion driven by an intense femtosecond laser pulse interaction with the gas clusters

With the development of femtosecond (fs) laser technology, an fs laser pulse with 10s of Joule, even 100s of Joule energy is available and the focused laser intensity can be expected to induce the pure Coulomb explosion of the cluster with a much larger average radius than before. Meanwhile, the production of gas cluster with an average radius of upto 10s of nanometer has been possible. In this case, it is necessary to reinvestigate the feasibility of 109 n/shot neutron yield for the practical application in the intense fs laser-driven nuclear fusion. In this work, the neutron yield from the explosions of the D2 clusters of 6–20 nm average radius at the 0.5–100 J pulse energy and the CD4 clusters was investigated theoretically. It is found that the optimum neutron yield of 109 n/shot can be obtained at the laser energy and the cluster radius currently available. However, a clustered-gas jet with a large cross-section is demanded to match the proper plasma diameter.

Application of the screened Coulomb potential to fit the DA-type variable star HS 0507 + 0434B

ABSTRACT wdec is used to evolve grids of DA-variable (DAV) star models adopting the element diffusion scheme with pure and screened Coulomb potentials. The core compositions are thermonuclear burning results derived from mesa. mesa yields composition profiles that the version of wdec used in this work could not accommodate (most notably, the presence of helium in the core of the model). According to the theory of rotational splitting, Fu and colleagues identified six triplets for the DAV star HS 0507 + 0434B based on 206 h of photometric data. The grids of DAV star models are used to fit the six reliable m = 0 modes. When adopting the screened Coulomb potential, a best-fitting model of log(MHe/M*) = −3.0, log(MH/M*) = −6.1, Teff = 11 790 K, M* = 0.625 M⊙, log g = 8.066 and σRMS = 2.08 s was obtained. Compared with adopting the pure Coulomb potential, the value of σRMS is improved by 34 per cent. This study may provide a new method for research into mode-trapping properties.

Two-body corrections to the g factors of the bound muon and nucleus in light muonic atoms

A nonrelativistic (NR) theory of recoil corrections to the magnetic moments of bound particles is revisited. A number of contributions can be described within an NR theory with the help of various potentials. We study those potential-type contributions for two-body atomic systems. We have developed an approach, that allows us to find the g factor for an electron or muon in a two-body bound system for an arbitrary electrostatic interaction together with the m/M recoil corrections, as well as the binding corrections to the g factor of the nucleus. We focus our attention on light muonic two-body atoms, where the recoil effects are enhanced. Both mentioned kinds of contributions have been previously known only for the pure Coulomb effects. We have applied the here-obtained master equations to a few particular cases of perturbations of the Coulomb potential. In particular, the results on the recoil corrections to the finite-nuclear-size (FNS) and Uehling-potential contributions to the g factor of the bound muon are obtained. The Uehling-potential and FNS contributions to the g factor of the bound nucleus have been found as well together with the related recoil corrections. We have generalized the results for the case of the g factor of a bound muon in a three-body atomic system consisting of an electron, a muon, and a spinless nucleus. Graphical abstract

Dynamics of Bladed Disks With Frictional Coupling and Alternate Mistuning Pattern

In the field of turbo machinery design frictional coupling has been found to be a low cost method to increase the mechanical damping of bladed disks. Underplatform dampers (UPD’s) are commonly used which are metal devices pressed against the blades by centrifugal forces. The main task is to find the optimum value of the contact normal force to maximize energy dissipation. This optimum strongly depends on the excitation of the structure. Traveling waves are excited by engine order excitation and flutter. Flutter caused by fluid structure interaction can be reduced by intentional mistuning of the bladed disk whereas forced response levels will be typically increased by mistuning. A compromise is alternate mistuning. The present paper deals with the influence of alternate mistuning on frictional coupling of blisks. Firstly, the dynamics of a tuned blisk are explained with a simplified lumped mass cyclic oscillator model. It is pointed out that eigenfrequencies of traveling waves around the blisk are influenced by structural coupling. Alternate mistuning leads to mode coupling with the possibility of energy transfer. The performance of friction coupling strongly depends on the nodal diameter mode shape of vibration which is stated analytically for pure Coulomb sliding contact. Following this, a simplified blisk model with underplatform dampers is developed to analyze alternate mistuning and frictional coupling. The simulation results show a significant influence of the mistuning on the damping performance.

Two Approximate Analytic Eigensolutions of the Hellmann Potential with any Arbitrary Angular Momentum

The parametric Nikiforov-Uvarov (pNU) and asymptotic iteration method (AIM) are applied tostudy the approximate analytic bound state eigensolutions (energy levels and wave functions) of theradial Schr¨odinger equation (SE) for the Hellmann potential which represents the superposition ofthe attractive Coulomb potential (-a/r) and the Yukawa potential bexp(-δ/r)/r of arbitrary strengthb and screening parameter d in closed form. The analytical expressions to the energy eigenvalues Enlyield quite accurate results for a wide range of n; l in the limit of very weak screening but the resultsbecome gradually worse as the strength b and the screening coefficient d increase. The calculatedbound state energies have been compared with available numerical data. Special cases of our solutionlike pure Coulomb and Yukawa potentials are also investigated.

Fictitious-Time Wave-Packet Dynamics in Atomic Systems

Gaussian wave packets (GWPs) are well suited as basis functions to describe the time evolution of arbitrary wave functions in systems with non-singular smooth potentials. They are rare in atomic systems on account of the singular behaviour of the Coulomb potential.We present a time-dependent variational method that makes the use of GWPs possible in the description of propagation of quantum states also in these systems. We use a regularization of the Coulomb potential and introduce a fictitious-time coordinate in which the evolution of an initial state can be calculated exactly and analytically for a pure Coulomb potential. Therefore, in perturbed atomic systems variational approximations only arise from those parts of the potentials which deviate from the Coulomb potential. The method is applied to the hydrogen atom in external magnetic and electric fields. It can be adapted to systems with definite symmetries and thus allows for a wide range of applications.